Potential Importance of Binary Evolution in UV-Optical Spectral Fitting of Early-Type Galaxies

TL;DR

This study highlights the significance of including binary star evolution in spectral fitting models for early-type galaxies, revealing substantial impacts on derived galaxy parameters and star formation histories.

Contribution

It introduces a stellar population synthesis model that incorporates binary evolution, demonstrating its influence on spectral fitting results for early-type galaxies.

Findings

Binary inclusion alters galaxy age estimates, especially for young stellar components.

Models with binaries suggest older ages for young populations compared to single star models.

Binary models lead to larger inferred dust extinctions, reducing the need for negative extinction values.

Abstract

Binaries are very common in galaxies, and more than half of Galactic hot subdwarf stars, which are thought as a possible origin of UV-upturn of old stellar populations, are found in binaries. Previous works showed that binary evolution can make the spectra of binary star populations significantly different from those of single star populations. However, the effect of binary evolution has not been taken into account in most works of spectral fitting of galaxies. This paper studies the role of binary evolution in spectral fitting of early-type galaxies, via a stellar population synthesis model including both single and binary star populations. Spectra from ultraviolet to optical band are fitted to determine a few parameters of galaxies. The results show that the inclusion of binaries in stellar population models may lead to obvious change in the determination of some galaxy parameters and therefore it is potentially important for spectral studies. In particular, the ages of young components of composite stellar populations become much older when using binary star population models instead of single star population models. This implies that binary star population models will measure significantly different star formation histories (SFHs) for galaxies compared to single star population models. In addition, stellar population models with binary interactions measure larger dust extinctions than single star population models on average. It suggests that when using binary star population models instead of single star population models, negative extinctions are possibly unnecessary in spectral fitting of early-type galaxies.